1. Field of the Invention
The present invention relates to a self-propelled and steerable airship (a so-called "dirigible").
2. Related Art
Conventionally, large airships have been made with buoyant gas held in gas bags contained within a rigid elongated enclosure; this requires a fairly complex structure which is expensive to build. Also, such structures are subject to high stress when windy or stormy conditions are encountered, and when landing and taking off, and there have been disastrous failures of airship structures in these conditions. The stress problems become more serious as the size increases, partly due to well known effects of scaling up structures, and partly because the effect of wind shear increases with the length of the airship. Small airships, the so-called blimps, are made without any rigid structure but these cannot be made in an ideal streamlined shape and are structurally unsafe beyond a certain size.